The present invention is related to an improved controlling mechanism of a pneumatic tool, and more particularly to a controlling mechanism in which the valve of the intake structure and the forward/backward operation switching structure are modified to enhance the utility of the pneumatic tool.
FIGS. 4 to 7 show a conventional controlling mechanism of a pneumatic tool. The pneumatic tool has a main body 7 formed with an inlet passage 71 through which air flows into a pneumatic motor disposed in the main body. A flow regulating button 72 is radially disposed in the inlet passage 71. The flow regulating button 72 is coaxially connected with a direction switching button 73. One end of the direction switching button 73 protrudes from the main body 7 and is connected with a shift bar 74 for driving the direction switching button 73 so as to switch the pneumatic tool between forward operation and backward operation. The direction switching button 73 is formed with an axial valve opening 75. A valve rod 76 axially extends into the valve opening 75. One end of the valve rod 76 extends out of the main body 7 and is pushed by a press lever 77. The other end of the valve rod 76 is pushed by a spring 78 disposed in the flow regulating button 72, whereby a washer 79 blocks the valve opening 75.
In operation of the conventional controlling mechanism, the air first gets into the flow regulating button 72. When the press lever 77 is pressed to drive the valve rod 76, the valve rod 76 is pushed away from the valve opening 75, whereby the air in the flow regulating button 72 will enter the direction switching button 73. At this time, in accordance with the forward or backward operation adjusted and set by the shift bar 74 of the direction switching button 73, the air will enter the pneumatic motor 8 to drive the same to forward operate or backward operate. When the press lever 77 is released, the valve rod 76 is pushed by the spring 78 to make the washer 79 block the valve opening 75.
The shift bar 74 protrudes from one side of the main body 7 so that the shift bar 74 is subject to collision and breakage. The shift bar 74 is disposed between the press lever 77 and the main body 7 for driving the direction switching button 73. After the direction switching button 73 is rotated, one of two air conducting holes 81, 82 is aligned with and communicates with the air inlet 83 of the pneumatic motor 8. The two air conducting holes 81, 82 have a certain diameter for necessary amount of air. Therefore, the central lines of the two air conducting holes 81, 82 must contain an angle of 90 degrees so as to truly separate the incoming air from the outgoing air. Therefore, when using the shift bar 74 to change the operation direction of the pneumatic motor 8, it is necessary to rotate the shift bar 74 by 90 degrees. As a result, the shift bar 74 should not be too wide. Moreover, in order to avoid leakage, a washer 79 (O-ring) must added to the direction switching button 73 driven by the shift bar 74. This leads to resistance against rotation of the direction switching button. Therefore, the shift bar 74 must have a considerable length, that is, the length (application force arm) of the shift bar 74 should not be too short. Due to the above factors of width, length and position of the shift bar 74, the shift bar 74 is easy to be broken.
Furthermore, the valve rod 76 is positioned in the direction switching button 73 and extends through the valve opening 75. Therefore, in design, the diameter of the valve rod 76 is limited. As a result, the washer 79 for blocking the valve opening 75 should not be too coarse. Therefore, after continuously opened and closed, the washer 79 is subject to wear. This will lead to leakage of air.